MnO2 nanosheet-based heparin and OSCS fluorescent biosensor with lowered background and amplified hybridization chain reaction

Abstract

We report a “turn-on” ultrasensitive method with ultralow background for heparin or OSCS detection in aqueous solutions. The signal amplification was realized by a hybridization chain reaction (HCR). The background was lowered by the quenching effect of MnO₂ nanosheet. MnO₂ nanosheet served as an efficient fluorescence quencher to reduce the background signal. It was used as a platform for absorbing the single-stranded DNA (ssDNA) while desorbing double-stranded DNA (dsDNA). In the presence of the target analytes, the HCR process would happen. The long chain dsDNA would detach from the surface of MnO₂ nanosheet. The fluorescence of SYBR Green I (SG I) inserted in dsDNA cannot be quenched. Therefore, a signal-on mode was employed in the signal-amplified and background-lowered fluorescence sensor. This can increase the biosensing reliability and overcome the disadvantages of susceptibility to false positive response or inferior sensitivity. In the heparin biosensing system, the sensor exhibits high sensitivity with a linear range from 10⁻⁵ to 1 μM and a detection limit of 4 pM. In the OSCS detection process, the linear range is 10⁻¹⁰% to 10% w/w and the detection limit reaches 10⁻⁸% w/w. The sensor shows enhanced sensitivity, stability and reproducibility in sample analysis. In addition, the quenching effect of MnO₂ nanosheet toward SG inserted into double-stranded DNA (dsDNA) was not studied in this work. The MnO₂ nanosheet-SG holds great promise as a simple and background-lowered novel fluorescent biosensing platform that may be extended for other related analytes.